As a voltage-type DC grid is expected to be needed, a short accident current breaking time is required. As measures to the requirement, WO 2011/057675 A1 discloses a hybrid DC breaker by ABB in 2011.
The disclosed hybrid DC breaker is configured as a combination of mechanical switches and power semiconductor switches, so that short breaking time and relatively-small normal-state conduction loss in accordance with the requirements may be secured.
In the structure of the hybrid DC breaker, since a portion of performing main breaking of a current commutated in the main conduction path is configured with a power semiconductor breaker, power loss does not occur in a normal conduction state. However, since a rated voltage thereof needs to be higher than a rated voltage of an application system, in the case where the hybrid DC breaker is applied to a super-high-voltage DC transmission (HVDC, High Voltage Direct Current) system, a large number of power semiconductor elements are needed. There is a problem in that this causes the structure of the breaker system to be complicated, and thus, cost is largely increased. Since the power semiconductor breaker has directionality in current conduction, in the case where the bidirectional breaker is configured, economical burden is further increased. In addition, although an auxiliary power semiconductor switch applied to a main conduction unit is also configured with a small number of power semiconductors, since the switch performs a function of conducting a rated current in a normal state, in comparison with a mechanical switch, power loss occurs in the power semiconductor switch, and a cooling system for the power semiconductor switch becomes a burden. In addition, since a capacity for a surge current at the time of closing is limited, there is a problem in that many factors needs to be considered at the time of application to actual system.